Etiology of tuberculous disease caused by acid-fast bacilli other than the classical species, Mycobacterium tuberculosis, M. bovis and M. avium is poorly defined. To provide a better understanding of the origin of human infections caused by non-classical species we are comparing strains isolated from the environment with those isolated from human and animal disease, from a genetic point of view. We are employing studies of the mechanisms of phage susceptibility including the provirus state and its control to indicate relatedness (or unrelatedness) of strains isolated from the two different sources. The results are being correlated with other characteristics such as enzymatic activities and antibiotic sensitivities to more clearly define kinship and other biological interrelationships which exist among this important group of microorganisms. We are also testing certain species of mycobacteria for the capacity to exchange genetic information by way of transformation, transduction and/or conjugation. An important segment of our research project concerns the repair of radiation damage in both mycobacteriophage and host genomes; efforts are being directed toward the isolation and characterization of products which cause the damage that leads to lethality and to identify possible mechanisms for reversing the damage. In addition, our study includes an investigation of the effects which temperature exerts upon phage susceptibility and virulence of certain species of mycobacteria. The results should tell us something of the mechanisms which control virulence, a phenomenon which is poorly understood but which is of prime importance.